Sharpness at 20mm

The sharpness tests for this review were carried out using a real-world subject rather than a test chart. The Canon EF 16-20mm f/4L IS USM lens was attached to a Canon EOS 5D Mark IV body, which in turn was mounted on a sturdy tripod. Self-timer mode was activated. Slight tonal changes are due to slight changes in natural light during the session.

The full frame at 20mm

Center and edge sharpness are excellent wide-open at f/2.8 and nothing short of outstanding between f/4 and f/11. At f/22 sharpness across the frame is beginning to drop-off due to diffraction, but is still commendably high.